1. Field of the Invention
This invention relates to non-impact printheads which are used for recording on photosensitive recording surfaces by electro-optical means such as light-emitting diodes (LED's) and other light sources. The invention further relates to a method for making such printheads to provide balanced light outputs by the recording elements.
2. Description Relative to the Prior Art
In the prior art as exemplified by U.S. application Ser. No. 07/375,154, an LED (light-emitting diode) printhead is disclosed wherein the problem of nonuniformity of light output from the LED's is recognized. Each printhead may include several thousand LED's arranged in a row. When the LED's are driven with the same levels of electrical current, some of the LED's are found to provide more light output than others, thereby providing nonuniformity between their respective exposures on the recording surface. To overcome this problem, the patent application discloses that a mask may be provided between the LED's and the recording surface. The mask comprises a layer containing a fadeable dye that has been exposed by an ultraviolet emitting-light source. The density of the portion of a mask opposite a respective LED varies with the brightness of that LED so that correspondingly more light is absorbed in masked portions opposite brighter LED's. Thus, uniformity in light output is achieved or at least improved. However, the use of the mask reduces the effective amount of light-impinging on the photosensitive recording surface from that LED.
It is an object, therefore, of the invention to provide for improved uniformity in LED printheads or the like without the noted disadvantages of the prior art.